Tidal disruption events: Progress, open questions and prospects

A tidal disruption event (TDE) occurs when an ill-fated star wanders too close to a supermassive black hole (SMBH), and is torn apart by tidal forces.  TDE observations offer a unique laboratory to measure SMBH masses and to study super-Eddington accretion and associated outflows.  In radio wavelengths, observations can allow us to probe the environment around previously-dormant SMBHs, as well as the physical properties of the outflow itself.  To date, ~100 TDEs are known, the majority of which are discovered by optical surveys and then followed-up at other wavelengths.

Recently, it has become apparent that some TDEs can indeed exhibit delayed onset of radio emission, which may be due to the long-elusive off-axis jets, or to a previously unknown delayed phase of TDE accretion and outflows.  For example, in the recent case of AT2018hyz, the outflow began several hundred days post-disruption, at mildly relativistic speeds.  In this talk, I will first give an overview of the TDE phenomenon, and observations to date.  I will also discuss the phenomenon of late-time radio emission, including results from a radio survey using the VLA and MeerKAT of ~25 TDEs >2 years post-disruption, which did not exhibit radio emission at early times. I will discuss the rate of radio-bright TDEs at late times, and implications for the density profile surrounding SMBHs.